1. Field of the Invention
The present invention relates to a method and system for the partial oxidation of isobutene having reduced methacrolein, methacrylic acid and acetic acid losses.
More particularly, the present invention relates to methods and systems for the partial oxidation of isobutene including the steps partially oxidizing an isobutene stream into a crude methacrylic acid containing stream in an oxidation subsystem. The crude methacrylic acid containing stream is instantaneously or near instantaneously quenched with a sufficient amount of a recycle stream in a sump portion of a quench column of a quench/distillation subsystem, sending a first portion of a bottoms product for methacrylic acid and acetic acid separation and purification, recycling a second and major portion of the bottoms product as the recycle stream to quench the crude methacrylic acid containing stream, sending a portion of an overhead product from the quench/distillation subsystem to a methacrolein recovery or absorber/stripper subsystem, recycling a major portion of the bottom stream from the stripper column to an upper portion of the absorber column and forwarding a recovered methacrolein stream from the overhead of the stripper column to the oxidation subsystem.
2. Description of the Related Art
Many patents and publications disclose aspects of a process of partially oxidizing isobutene or an isobutene equivalent into methacrylic acid in a single step or multi-step oxidation process. Some of these patents related directly to or extensively discuss quenching of the effluent from the partial oxidation of the isobutene or isobutene equivalent input stream.
In U.S. Pat. No. 4,554,054 disclosed a process to recover acrylic acid or methacrylic acid by using a split quench process which allows acrylic acid or methacrylic acid to be recovered from the resulting aqueous solutions by a combination of solvent extraction and azeotropic dehydration that minimizes the amount of solvent required.
In U.S. Pat. No. 4,618,709 disclosed a process for separation of methacrylic acid from a methacrylic acid-containing, gaseous reaction mixture obtained by subjecting methacrolein or a compound which can afford methacrolein under reaction conditions and molecular oxygen to gas phase reaction in the presence of a catalyst for oxidation under the coexistence of an inert gas for dilution which comprises (a) cooling the gaseous reaction mixture from a reactor wherein the gas phase reaction has been effected to separate into condensable components including methacrylic acid, acetic acid and water vapor as a condensed liquor and non-condensable components including methacrolein as anon-condensed gaseous mixture, (b) eliminating contaminating methacrolein from the condensed liquor and (c) contacting the resulting condensed liquor with an organic solvent to extract methacrylic acid, followed by separation into an organic solvent solution including methacrylic acid and an aqueous solution as waste water, characterized in that (1) the inert gas for dilution is a non-condensable gas or its mixture with water vapor and (2) the aqueous solution ultimately separated is evaporated and the evolved vapor is subjected to catalytic combustion with molecular oxygen, whereby the amount of waste water to be discharged is much suppressed.
In U.S. Pat. No. 4,925,981 disclosed a method of isolating and recovering methacrylic acid from a methacrylic acid-containing reaction product gas resulting from the vapor-phase catalytic oxidation of isobutylene, tertiary butanol or isobutyraldehyde, which comprises introducing the reaction product gas comprising methacrylic acid and various by-products including high boiling substances at a high temperature of 250° to 300° C. into a cooling zone, rapidly cooling the gas therein to a temperature of not more than 100° C. to condense methacrylic acid and thus isolate methacrylic acid, while also converting the high boiling substances to fumes, thereafter introducing the cooled gas containing said fumes into a venturi scrubber, contacting it therein with an aqueous medium to remove said fumes, finally introducing the treated gas into a methacrylic acid-absorbing zone and absorbing methacrylic acid by absorption into an aqueous medium.
In U.S. Pat. No. 4,956,493 disclosed a process for producing a methacrylic ester which comprises catalytically oxidizing isobutylene, tert-butanol, methacrolein or isobutyl aldehyde in a vapor phase; removing light-boiling substances form the resulting reaction product by distillation or stripping; extracting methacrylic acid from the resulting methacrylic acid aqueous solution using a saturated chain aliphatic hydrocarbon having 6 to 9 carbon atoms as a solvent; recovering the solvent from the obtained solvent solution of methacrylic acid; esterifying the resulting methacrylic acid by the reaction of it with a lower aliphatic alcohol or a lower alicyclic alcohol having 1 to 12 carbon atoms using a porous strongly acidic cation exchange resin as a catalyst for esterification; and then subjecting the thus obtained esterification reaction product to a purification step.
In U.S. Pat. No. 4,987,252 disclosed in order to recover methacrolein and/or methacrylic acid by quenching a reaction product gas obtained by catalytic oxidation of isobutylene or the like, the reaction product gas is charged into a quench column through a double-wall pipe and is then brought into contact with a condensate as a cooling medium. Deposition of terephthalic acid and the like inside the column is prevented by controlling the temperature of a bottom in the quench column and that of an overhead gas of a quench column unit. An aromatic carboxylic acid, aromatic aldehyde, metal powder is added to an aqueous solution of methacrylic acid, which contains terephthalic acid and the like, so that the terephthalic acid and the like are caused to precipitate for their removal.
In U.S. Pat. No. 5,356,460 disclosed methacrolein is removed from a gaseous mixture by absorption by means of an aqueous solution which contains from 60 to 90% by weight of methacrylic acid.
In U.S. Pat. No. 5,780,679 disclosed a process for the separation of (meth)acrylic acid from the reaction gas mixture formed in the catalytic gas phase oxidation by countercurrent absorption using a high-boiling inert hydrophobic organic liquid, in which the reaction gas mixture is passed through an absorption column countercurrently to the descending high-boiling inert hydrophobic organic liquid and (meth)acrylic acid is subsequently fractionally separated from the liquid effluent leaving the absorption column and containing (meth)acrylic acid, wherein a rectifying process is superimposed on the absorption process occurring naturally in the absorption column by removing a quantity of energy from the absorption column which exceeds its natural energy loss resulting from contact with the ambient atmosphere.
In European Patent No. 0345083 B1 disclosed a process for recovering methacrolein which comprises: a reaction step (A) comprising catalytically oxidizing isobutylene, t-butanol, methacrolein, isobutyl aldehyde or isobutyric acid or a mixture thereof with a gas containing molecular oxygen in a vapor phase, a methacrylic acid condensation step (B) comprising contacting the reaction product gas obtained in step (A) with an aqueous phase containing methacrylic acid and acetic acid to obtain an aqueous solution of methacrylic acid, a methacrylic acid extraction step (C) comprising extracting methacrylic acid (page 24, lines 11 and 12) obtained in step (B) with an extraction solvent which is a saturated hydrocarbon having 6 to 9 carbon atoms, and separating the extracted methacrylic acid to a solvent phase and an aqueous phase containing acetic acid, a methacrolein recovery step (D) comprising contacting the gas containing methacrolein and methacrylic acid discharged from step (B) with an aqueous phase containing methacrylic acid and acetic acid to recover methacrolein and methacrylic acid contained in said gas into said aqueous phase, a methacrolein desorption step (E) comprising contacting the aqueous phase containing methacrylic acid, acetic acid and methacrolein discharged from step (D) with a gas containing molecular oxygen to desorb methacrolein, and a methacrylic acid recovery step (F) comprising contacting the gas containing methacrylic acid and methacrolein desorbed from step (E) with an aqueous phase containing acetic acid to obtain a gas containing methacrolein, at the same time recovering methacrylic acid into said aqueous phase, which process comprises circulating the aqueous phase containing acetic acid discharged from the methacrylic acid extraction step (C) in the methacrylic acid recovery step (F), circulating the aqueous phase containing methacrylic acid and acetic acid discharged from the methacrolein desorption step (E) in the methacrylic acid condensation step (B) and/or the methacrolein recovery step (D) and circulating the gas containing methacrolein discharged from the methacrylic acid recovery step (F) in the reaction step (A).
Although these patents and publications disclose many different processes and equipment for achieving a rapid quenching and processing of the oxidation effluent, there is still a need in the art for a system and a related process that rapidly quenches the oxidized effluent while achieving reduced methacrolein, methacrylic acid and acetic acid losses.